Spatial distribution analysis of landslides triggered by the 2013-04-20 Lushan earthquake, China

Abstract

The 2013-04-20 Lushan earthquake (seismic magnitude Ms 7.0 according to the State Seismological Bureau) induced a large number of landslides. In this study, spatial characteristics of landslides are developed by interpreting digital aerial photography data. Seven towns near the epicenter, with an area of about 11.11 km2, were severely affected by the earthquake, and 703 landslides were identified from April 24, 2013 aerial photography data over an area of 1.185 km2. About 55.56% of the landslide area was less than 1000 m2, whereas about 3.23 % was more than 10,000 m2. Rock falls and shallow landslides were the most commonly observed types in the study area, and were primarily located in the center of Lushan County. Most landslide areas were widely distributed near river channels and along roads.Five main factors were chosen to study the distribution characteristics of landslides: elevation, slope gradients, fault, geologic unit and river system. The spatial distribution of coseismal landslides is studied statistically using both landslide point density (LPD), defined as the number of landslides (LS Number) per square kilometer, and landslide area density (LAD), interpreted as the percentage of landslides area affected by earthquake. The results show that both LPD and LAD have strong positive correlations with five main factors. Most landslides occurred in the gradient range of 40°-50° and an elevation range of 1.0-1.5 km above sea level. Statistical results also indicate that landslides were mainly formed in soft rocks such as mudstone and sandstone, and concentrated in IX intensity areas.